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In October 2002, I reviewed the Ashtech Locus L1 GPS system for another magazine. The Locus, an L1 or single-frequency system, was combined with Solutions processing software to provide surveyors with a very cost effective entry into the GPS arena. Many Locus units have been in use daily ever since. At that time I met Bill Martin, and it is what has occurred in the interim that brings us to the subject of this column, the EPOCH 10 from Spectra Precision. Martin is now with TDS, a Trimble Company, that sells and distributes Spectra Precision Survey Products.
While I have not investigated the connection between Martin and the EPOCH 10, his influence is unmistakable in my perception, as are the benefits and feedback garnered from the users of these single-frequency GPS systems. This knowledge is evident in the EPOCH 10, a new L1 system for static and post-processed kinematic GPS. It consists of the Spectra Precision Recon data collector loaded with TDS Interlock Geodetic Controller software; the EPOCH L1 GPS receiver and antenna; and Spectra Precision Survey Office software. EPOCH 10 will be a welcome addition to the single-frequency equipment presently available. (Note: the Epoch 10 system can also run on a Recon you may already own.)
The GPS receiver is a 12-channel L1 C/A Code, L1 Full Cycle Carrier that is WAAS/EGNOS capable. The WAAS/ EG NOS capability is software application dependent. The Recon with the GPS Receiver-Cap attached is approximately 3.7" x 1.7" x 9.5" and has been tested to IP6X standards for sand and dust and to IPX7 standards for water penetration. Shock and vibration have been tested to MIL-STD-810-F, meaning it will stand up to use by the military. It will work from -22º F to +140º F and in 100% humidity. The antenna is 2.44" high x 6.38" diameter, weighs less than a pound, and will operate from -122º F to +185º F. The specifications also mention "multipath" mitigation, and it does indeed have improved multipath capability based on the point "maps01" in my back yard.
The units were shipped to my home as they would have been to a dealer, therefore I had to perform some assembly to ready the units for the purpose of reviewing them and writing this article. A Quick Reference Card explains what to do, and how and when to do it. First the "Powerboot" Module, or battery, has to be attached to the Recon and then charged. Please permit a slight digression here. Spectra Precision Survey advises the purchase of spare "Powerboot" Modules – sage advice that needs to be heeded, especially for those of us in the colder climates. There was snow on the ground and the temperature was hovering in the 30’s when I was in the field. At the end of five and a half hours the main battery of the base unit was down to 20% remaining.
Next the standard "CF-Cap" is unscrewed, removed and then replaced with the extended cap base. Then the cap base is inserted and secured with the half turn locks using the stylus or a screwdriver. The cap base is actually the housing for a GPS/compact flash card receiver, which is the next component to be put on, but a word of caution is needed here. You must take care to properly align the receivers CompactFlash interface with the slots in the Recon.
When the proper procedure was followed, the GPS CF card slid into place with only a slight push to seat it home. Turning the locking screws on each side of the cap with the combination stylus/screwdriver blade completes the assembly. Set the units to charge and you are good to go!
Part of the package is the Spectra Precision Survey Office software. This is the software that post-processes your static and post-processed kinematic (PPK) field sessions. I’ll get into it later in this article, but do read/print the release notes.
Page 4 gives the default location for all your data, project, and how export files are stored. Storage is in the "My Documents" section of your computer. Instructional post-processing video tours are available too!
NGS control is sparse in my neck of the woods, so I checked into the PennDOT PAMS site and found four recent marks within three miles of my home (a good way to try the EPOCH 10, I thought.) One unit would be set on a point in my yard, a secure location, and I would occupy two of the PennDOT marks for 30 minutes.
Using my prism poles and bipods I began with the "base" in the back yard, not exactly the ideal GPS location (Figure 1). You can see that the antenna cable plugs into the GPS/CF card cap at the top. Note the inch of cable protector on the 1-1/2" molded plug. This design goes a long way in preventing "kinking" of the cable or "stretching" of the cable when inserting or removing it. It is also a convenient place for the fingers, instead of yanking on the cable alone. Kinked or stretched cables lead to unseen breaks in the wires, which results in intermittent data transfer and finally no data transfer at all.
I grabbed the TDS Interlock Geodetic Controller software "Quick Start Guide", all seven pages of it, and turned to "starting a job" and then "starting a static survey". In each case I followed the few steps and was up and running. Just that quick and just that simple! In retrospect, I would have set up my style first, loaded a portion of a USGS Quad and navigated to the mark. That is the way I would set up these units for the field crews. So far, so easy, and so good!
On to PennDOT J201 and the next setup (Figures 2 and 3). The blue crate upon which I placed the Recon may not have been particularly attractive, but it was a safe place for the controller. It even attracted the attention of a Pennsylvania State Trooper who slowed for a look, saw me across the ramp with my magnetically mounted revolving amber roof light, waved, and then continued on.
At the other cable end are two inches of a molded cable protector and a metal right angle connector to the antenna (Figure 4). The designer is working with, not against, gravity with this arrangement. Following the simple instructions of the Quick Start Guide I was up and running again. That is all the reading that I did to get underway with the EPOCH 10 system and successfully collect GPS sessions. If you are in a secure area, you can even preprogram the Recon for the length of your data recording and have it shut off automatically. In these sessions I manually shut them off after 30 minutes, which you can time or bring up a log on the Interlock software. There is even a check box to enable WAAS.
Back to the house and the office software for some post-processing with Survey Office. In order to use the office software you must have a dongle (hardware lock) that uses one of your USB ports. Due to my past experience with "hardware locks" I have developed a definite bias against them. My preference would be some type of software scheme as many software vendors provide today. I can say that this one performed flawlessly with no issues at all, so perhaps I should update my experience and opinion of them.
One of the pages in the release notes has a list of the file types supported by Spectra Precision Survey Office (Survey Office). ASCII point files, AutoCAD *.dwg and *.dxf, files can be imported and exported. NGS Data sheets and RINEX files can be imported but not exported. *.job files can also be exported from the Recon to TDS Survey Pro 4.x in order for you to use your GPS points in combination with conventional equipment on your jobs.
You can get a glimpse into the future of Survey Office when you enter the planning module. The usual selection of DOPs is there, but in addition to the GPS check box there is one for GLONASS and
one for WAAS. Anybody want to bet on how soon one will be added for Galileo? How about a side bet for the Interlock implementation of these choices?
Take advantage of the USB ports of the Recon and your PC with Office Synchronizer software to transfer your GPS sessions into Spectra Precision Survey Office. The speed of the USB port is ten times faster than a serial port transfer according to the literature, but the InterLock software still has a serial port available for people who have older systems too. This is another example of the benefits of prior design experience and user feedback. The actual transfer involves Microsoft Active Sync, too! Highlight the files for the sessions you need using the import command from the drop-down menu under the "Project" command on the toolbar. Click "OK" and if you are like me you will then do a "Save" before you begin the processing of your data.
Next I checked the raw data file antenna heights and start and stop times against the session sheets. Make sure that if you have selected, say meters, for your project units, you enter the proper antenna heights, if you did not already do so in the Recon when you started your session. When you are satisfied with your data, process your baselines by using either the menu or the icon on the toolbar. Then watch your vectors appear on your plan view. You can click on any one for its data or go to the reports section and print out reports of them. In similar fashion you can adjust your network. In this instance I was more interested in baselines and raw positions in comparison to the published positions of the points I used.
For instance, from J198 to maps01 my standard errors on this vector were 0.003m northing, 0.002m easting, and 0.004m elevation. The inversed distance from J198 to J201 as published is 6,798.91 feet. My raw, unadjusted values for these same two observation points was 6,798.86 feet. A difference of 0.05 feet over the 6,798.91 feet yielding a relative precision of 1:120,219. I probably had about 0.002m in each setup alone. I just used the processed baseline with no trimming of cycle slips, loss of lock or barely used SVs. This is most impressive to me considering these factors and an occupation time of only 30 minutes on each. Try looping a conventional traverse of at least 6,799 feet each way and see how far you get in a half hour.
Just think what you could do with more experience with this system! My short time with the EPOCH 10 system was very pleasant, positive, and left me with the perception that there is lot more to this L1 GPS system than I could glean from this brief experience. So, as I advise often, try it out for yourself and form your own opinion. Now more than ever is the time to add GPS capability to your tools if you have not already done so.
Al Pepling is a Project Surveyor with Monaloh Basin Engineers in Pittsburgh. He is licensed as a professional land surveyor in Pennsylvania, as a professional planner in New Jersey, and is a past president of the New Jersey Society of Professional Land Surveyors (NJSPLS).
A 1.308Mb PDF of this article, complete with images, may be downloaded by clicking HERE